40	LIFE  OF
the soil above the sea, aroused in Humboldt that
great interest in the geographical diffusion of plants
and animals, which., by his continued researches in Ame-
rica., made him entitled to rank as the first scientific
founder of this study. How important the influence
of altitude is on this propagation of plants he had
perceived already during his ascension of the cele-
brated peak of Tenerirfe. There he passed first
through the regions of tree-like heaths, then he came
higher up to a belt of ferns, higher still a wood of
juniper and fir trees ; over that was a plain two hours
and a half journey in breadth, covered with Spanish
broom, after which he came to the pumico-stone soil
of the volcanic crater, where he was welcomed by the
beautiful retama, with its sweet-smelling buds, and
the wild indigenous peak goat.
It might have been expected that Humboldt would
continue his geological studies here on the orator of a
volcano, and he did so most successfully, for lie col-
lected new materials for his subsequent observations
on, and explanations of, the volcanic influence in the
formation of the earth, and the phenomena of earth-
quakes.
A glance at the sea and the coast showed Hum-
boldt and Bonpland that their ship Pissarro was under
sail, and this alarmed them much, as they feared it
might prepare for departure without them. They
left the rock as speedily as possible, and rejoined their
ship., which had already waited for them to take Its
departure.
^ But Humboldt had gained important matter for
his   future   discoveries during  this   short   excursion.
The group of Canary Islands had become tin instruc-
tive book of infinitely rich contents, whoso diversity
in  a small space necessarily led a mind like Httm-
boldt's to further universal study.    He felt the true
mission of a naturalist, and the importance of special
research.    The soil on which we move in joy and sor-
row is the most mutable, most active in' destruction
and  reconstruction—a power rW«^  in it   which  ar«